Induction electric furnace



Oct. 11, 1932.

E. F. NORTHRUP INDUCTION ELECTRIC FURNACE 2 Sheets-Sheet l 7 Filed June 29. 1929 Oct. 11, 1932. E, NORTHRUP 1,881,888

' INDUCTION ELECTRIC FURNACE Filed June 29, 1929 2 Sheets-Sheet 2 Patented Oct. 11, 1932 UNITED STATES PATENT OFFICE EDWIN FITCH NORTHRU'P, OF PRINCETON, NEW JERSEY, ASSIGNOR TO AJ' AX ELECTRO- THERMIC CORPORATION, OF AJAX PARK, NEW JERSEY, A CORPORATION OF NEW JERSEY INDUCTION ELECTRIC. FURNACE Application filed. June 29,

My invention relates to electric circuits carrying alternating current or carrying 'fluctuating direct current.

One purpose of my invention is to equalize the flows or to maintain a predetermined proportion of flows of current through a plurality of parallel circuits substantially independently of the inductances, capacities and resistances within the individual circuits.

A further purpose is to pass circuits in parallel through equalizers comprising inductances so arranged as to be non-inductive when the currents passed through are equal or bear a predetermined relation, but which become inductive when the currents vary from equalities or these proportions, utilizing the induction thus setup to cut down the current to equality or the predetermined proportion.

A further purpose is to utilize the inductive effect of electric-current flow through inductances wound in parallel to maintain equality or a predetermined proportion of current flow through these circuits, sub-dividing the currents successively through such inductances in pairs to correspondingly multiply the number of circuits controlled.

A further purpose is to greatly increase the amount of current available through discharge gap circuits by reliably controlling the flow through the use of a plurality of gaps in parallel.

A further purpose is to pass currents in parallel through current equalizers or proportioners, using one equalizer or proportioner for one such current control and subsequently the individual currents thus controlled, using an equalizer or proportioner for each sub-division made and sub-dividing parallel currents in the same manner or differently as proves most convenient.

A further purpose is to pass parallel currents through coils having mutual induction, one upon the other, to utilize this mutual induction to make the individual coils noninductive and to use the self induction of the current in either branch, when the proportion of its current to that of the other increases above that intended, as a means to 1 929. Serial No.' 374,673.

tion between the currents flowing in the circuits.

A further purpose is to proportion the turns of mutually reactive coils in circuits in parallel in a reverse ratio to the currents which are intended to be passed through them and to make use of the equality of ampere turns thus secured to relieve the individual coils of inductance during flow of the currents contemplated and to utilize any variations of these currents as a means for the correction of the variation.

A further purpose is to fix any desired proportion between the currents in the circuits by inversely proportioning the number of turns in the equalizer coils.

A further purpose is to facilitate the operation of arcs in parallel.

Further purposes will appear in the specification and in the claims.

My invention relates both to the processes involved and to apparatus by which these processes may be carried out.

Ihave preferred to illustrate my invention Wholly diagrammatically in view of the broad character of the invention and to apply it to electric circuits generally rather than to those for a specific purpose because of the applicability of the invention to general uses.

Figures 1-14 are diagrammatic views showing the appliaction of my invention.

In many line's of electrical activity it is quite desirable to maintain equality of flows parity in the inductances, capacities or resistances involved. My invention equalizes current flows or maintains proportionate current flows not only in the variant conditions above but in all kinds of combinations of such conditions of kind or extent of circuit characteristics.

My invention is useful wherever it is desirable to maintain equality or a predetermined proportion between two or more alternating or fluctuating current circuits in which the constants of the circuits have considerable variation.

My invention is based upon application of the fact that when alternating or fluctuating currents are passed through circuits including inductance coils which are wound to gether so that the inductive effects of the coils tend to neutralize each other these inductive effects will automatically tend to equalize, making the products of the number of turns and the amperages of the respective coils equal. Both circuits are free from in ductance from the coils as long as the equality of ampere turns is maintained.

When current in one circuit through its coil increases above that needed to equalize the ampere turns in the other coil the inductance met by this increased current reacts to cut down the current. The control is thus automatic.

As later further illustrated, the portions of the circuits which are balanced or maintained in proportion may themselves, contain the load, or may contain a load auxiliary such as a discharge gap, for example, making the invention quit'e flexible and greatly enlarging its scope of usefulness.

In Figure 1 I show two lines 10 and 11 which may be alternating supply lines for the present purpose only, or which may feed a load not shown. Between these lines I pass the current in parallel through loads or auxiliary loads R R which may contain resistance, capacity or inductance, or any combination of these and in which the dominant constants may be the same or different in diiferent loads or auxiliary loads.

The parallel paths feeding these loads, or auxiliary loads pass through inductances L L so arranged that the inductance of each tends to negative the inductance of the other, resulting in a non-inductive current passage through each of the inductances so long as the currents through them are equal, or are inversely proportioned to the number of turns through the coils so as to equalize the ampere turns in each.

For convenience of nomenclature and because of the function performed I term the equalization or proportioning of the current flows. The equalizers are given the generic number 14.

The equalizer may be of the air core, 01' magnetic core type, as preferred.

serted within the several circuits at 13 which show the equality or relation of currents passing through the circuits to any degree of accuracy desired within ordinary limits of variation of the respective constants in the loads or auxiliary loads R or R Such indicators are a convenience rather than a necessity. They afford visible means for reassurance as to the operation of the circuits. The indicators need not be delicate nor accurate. Very satisfactory, rough indicators for the purpose may be supplied by nichromc strips of equal cross-section, or of section in suitable proportion to the currents which are intended normally to be carried.

lVhere it is intended that the currents through the two branches of the circuit shall be equal the number of turns of winding of the equalizer will be equal, but where it is the intention to have more current pass through one of these circuits than through the other the number of turns will be inversely proportioned so as to equalize the ampere-turns and hence the electromagnetic effects of the two coils.

Additional equalizers may be used where it is desirable to provide more than two circuits in parallel and to equalize the currents through them or proportion the currents according to a predetermined plan. I have shown four such circuits in Figure 2, arranged in a set of two pairs A and B, corresponding generally each to the pair shown in the equalized circuits of Figure 1. It will be evident that equality or a predetermined proportion of current will be maintained through the equalized pairs of circuits at A and B and their load circuits or auxiliary load circuits R It and R R by equalizers 14 14 including coils L L and L L and the desired equality or proportion of currents (total) through the individual pairs may be maintained by the equalizer 14 comprising coils L L Likewise in Figure 3 groups of sets may be handled just as sets of pairs are handled, the set F being grouped with the set E through. an equalizer 1 1 having coils L L Groups also can be handled through other equalizers and so on, the control being capable of indefinite extension along the same lines as the extension from the pair to the set, and the set to the group in the figures shown.

The. group F, as shown, comprises pairs C and D which feed loads or auxiliary loads R R and R R through equalizers 14, 14 made up of coils L L and L L The equalizer 14 is shown as provided with coils L and L and equalizer 14 comprises coils L L Throughout the different units the same thing is true that is true of the pair, namely, the pairs of the set need not have equal currents but can have proportionate currents which can, as indicated, then be divided in any way through the individual sets as may be desired. Also the sets of the group need not carry equal currents but can carry any proportion of current which can again be divided so that each individual path may carry any desired proportion of the total current, any inequalities thus produced in currentflows through the halves of a pair, or the pairs of a set, or the sets of a group, etc., being taken care of by proportioning the turns in the respectively controlling equalizers inversely to the quantitative'fiows of the currents which are to be handled by the respective paths;

Sources of current 10', 11' and 10 11 are shown in Figures 2 and 3 and any number of indicators 13 may be used.

The first impression from Figures 1 to 3 would be that the number of paths must be at least even and possibly two or a power of two. Neither is required. As seen in Fig- .ure 4 any single path through a pair or set 'or group can be substituted by a divided path fed from the same equalizer as the other (single) path of the pair, set or group.

In Figure 4 a circuit feeding a pair of loads such as in Figure 1 is split up to feed three loadsins'tead, shown at R R and R by the simple expedient of substituting another equalizer or controller 14 and two loads R and R for the load R If the coils of equalizer 14' have equal numbers of turns,in Figure 4, the loads R and R together will receive a total current equal to that'through the single load R However, if the number of turns in coil L be twice that in coil L and the numbersof turns in the coils of equalizer 14 be equal, the currents through all three loads will be equal.

Since this same scheme of division of one part of the circuit controlled by an equalizer can be applied to the division of the connection to one pair of a set, or one set of a group as easily as it is applied above to the connection of one load of a pair, and since the proportions of the currents passing through the branches of a pair, set or group can be controlled by selecting the number of turns of the coils of the equalizer, the system is unusually flexible.

So far the loads have been shown as if they were main loads rather than auxiliary loads; but there is no such limitation to the invention. Not only could the supply circuits 10, 11, 10','11, 10 11 contain other and main loads but other figures show the loads in parallel as auxiliary loads.

In Figure 5 I have applied my invention to the supply of current for a load R comprising an inductor coil which can be used charge gaps (loads) R and B in parallel without disturbance of the flow of current through the one by reason of flow of current through the other.

The current is supplied from any suitable source 10 11 having voltage E through a transformer 16 in which the primary is indicated at 17 and the secondary at 18. A choke,

coil 19 is included in the primary circuit to prevent the oscillations within the secondary circuit from afi'ecting the primary.

As the number of discharge gap paths in parallel can be increased as easily as the number of loads of any other character the invention makes it possible to operate any desired number of discharge gaps in parallel,

very greatly increasing the energy availablefrom this source for individual installations. I believe that I am the first to provide for operation of discharge gaps in parallel.

In Figure 6 a. construction is shown using a similar source of supply to that in Figure 5 and in which oscillatory current from the discharge of condensers is supplied to a furnace circuit.

A single discharge gap 20 is bridged across between the condensers and the transformer secondary and a plurality of individual loads such as are shown at R R R and R are located in parallel with each other but effectively in series with the inductor R These are all assured equal or properly proportional'currents and each shares in the benefit of being in circuit with the furnace reactance. The loads R R could be greatly increased in number if'desired. They can bear a relation to the inductor furnace,

as in the case of heating arcs, or be wholly independent sired.

In Figure 7 I have shown a construction comparable with Figure 6 in that auxiliary loads in parallel are shown in series with an of the Iurnace purpose as deinductor furnace coil, but difl'ering from Figure 6 radically in that the auxiliary loads in parallel are in series with both an inductor coil R and a condenser 15 in a tuned circuit across a line 10*, 11 A large current is provided, due to the current transformation effected by tuning the circuit. The auxiliary loads may be cut out through switch 21.

In a large furnace, for example, arcs represented by these loads can be used to play upon the surface of a pool heated by the coil or for any other collateral purpose.

In Figure 8 I have shown the same general connections as in Figure 5 except that each of the two discharge gap paths of that figure is represented here by two gaps R or R in series. Otherwise the parts have the same reference characters as in Figure 5.

In Figure 9 I have shown the lower part of Figure 5 with the difference however that I i have shown eight discharge gaps instead of two, using the arrangement of equalizers to maintain uniform current flow which is shown in Figure 3 and applying corresponding reference characters to them except that the discharge gaps are all referred to as R The permissible and indefinite extent of increase in the number of discharge gaps which can be used through my paralleling arrangement correspondingly increases the kilowattage available from discharge gap circuits.

In Figure 10 I haveshown the same form as in Figure 1 with the exception that the control or equalizer is shown as comprising coils L L one or both of whose inductions is or are adjustable by the use of taps in order that by adjustment of the induction of the coil or coils the ratio of current through the several paths may be altered. Obviously, the same adjustment of the coils-of the other equalizers may be efl ected in all of the forms if desired.

In Figure 11 I have shown a form corre sponding closely with that of Figure 6 except that the main load R has been omitted making the loads R R R and R main loads instead of auxiliary loads. What has been said of the Figure 6 and the capability of applying parallel discharge gaps in place of 20 is true of course also of Figure 10.

In Figures 12 and 13 the core and coreless types of reversely wound coincident coaxial coils L L. and L L are shown respectively, the number of turns being equal in Figure 11 and unequal in Figure 13. Of course, the core need not be straight and the coils need not overlap on the core, permitting the use of adjacent coils or a ring core if desired.

My equalizers are treated for the most part, as in Figures 11 and 12, for convenience as oppositely wound coaxial inductances. However, I do not wish by this to be understood as indicating that they must be coaxial nor oppositely wound, but only that they shall be so located and arranged as to permit flow of current through their coils in parallel, free from reactance and shall offer reactance to passage of current through either in excess of the equality or proportion of current designed to pass through it.

To illustrate the fact that the coils need not be wound oppositely I show in Figure 14 a duplex cable forming an equalizer. It is wound about the core 12' and the two conductors of the cable forming coils L and L are so connected that the current passes through them oppositely, securing the same effect as would be secured by opposite winding of the separate wires comprising the coils L and L Where the loads contain unequal positive or negative reactance the reactance of the equalizer coils must, of course, be large as compared with that of the loads so that low reactance or fluctuation of the load reactances will not unduly affect the total reactance.

In all of the forms the number of turns in the equalizer need not be as great for a higher frequency as for a lower frequency.

I have endeavored to point out in the above discussion, among other things, not only the general utility of my invention but its flexibility to supply and maintain equal or variant currents in parallel reliably to two or more circuits, or current paths, even or odd in number, whose circuit characteristics are of different value, or both; to show that the loads in these paths may be main loads or auxiliary loads related or unrelated to the main loads; that whether the loads are related or not they may benefit from the presence of a main load as in Figure 7 and take part of the energy of the main load circuit; and that what I have treated as an auxiliary load as in Figures 5 and 9, may be interrelated to the main load in such a way as to greatly increase the energy which can be supplied to the main load. This last offers a major benefit of considerable importance which may be considered as related to the general purpose of controlling the flow of currents through parallel circuits of unequal or variant reactance or resistance.

In View of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is 1. In an alternating currentcircuit, a main inductive load and a plurality of resistance loads in series therewith but in parallel with each other, including an equalizer for each pair of loads and for each pair of pairs, etc. of loads, each equalizer comprising induction coils having opposed inductive iary loads.

menses efiects, one in each auxiliary load circuit, adapted to neutralize each others inductance when the ampere turns of the coils in the equalizer are equal, condensers in series with the load circuit, a source of alternating current and a discharge gap across the source of current. 2. In an alternating current circuit, an inductor and a discharge gap source of alternating current therefor, the discharge gap having a plurality of gaps in parallel and equalizer means by which the currents through said gaps are controlled.

3. An inductor furnace coil and source of alternating current therefor, 'a plurality of discharge gaps in parallel across said source, condensers in series with said source and coil and equalizer means for controlling the current through said gaps.

4'. A source of alternating current, a main load, condensers between the source of current and the main load and discharge gap means across between the source and the condensers for permitting discharge of the condensers and comprising a plurality of pairs of discharge gaps in parallel and equalizer means in circuit with each pair and with each pair of pairs for maintaining the currents through the several gaps notwithstanding variation in the condition of the individual gaps. r

5. nace-and discharge gap means for furnishing oscillating current to the furnace inductor, the discharge gap comprising gaps in parallel and an induction coil in series with each gap, the coils being electromagnetically opposed and balancing each other when the ampere turns of the two coils are equal.

6. A source of alternating current, a transformer fed thereby and having a secondary, condensers in series with the secondary, a

furnace inductor in series said condensers and a discharge gap between the condensers and the secondary, across the second my and comprising a plurality of gaps and equalizer means for maintaining a predetermined relation of currents through the several gaps.

7. An alternating current circuit comprising a source of alternating current, a main load therefor, power factor correction for said main load forming a tuned circuit and an auxiliary load in series with saidtuned 'circuit and comprising a plurality of loads in parallel and equalizer inductive means for controlling the current through said aum'l- EDWIN F. NORTHBUP.

A coreless-type inductor electric fur 

